Suspension assembly

ABSTRACT

Hybrid suspension arm assemblies for use in magnetic head/arm assemblies utilize plastic components in conjunction with steel to provide excellent damping and rigidity. The hybrid suspension assembly requires much more input amplitude before resonance would become a problem.

FIELD OF THE INVENTION

This invention relates to magnetic recording and reading apparatus ofthe type including magnetic head/arm assemblies. More particularly, theinvention relates to novel suspension arm assemblies which are hybridsof plastic and steel.

BACKGROUND OF THE INVENTION

In magnetic head arm assemblies which are employed for radiallyaccessing different data tracks on rotating magnetic disks manydifferent forces may vary the spatial position of the head transducinggap relative to the data track that is being scanned. Heads experienceundesirable radial and circumferential forces as well as yaw moments.Head loads are on the order of 15 grams or less. The effect of radialand circumferential forces that are applied to the head arm must beminimized and yaw should be eliminated. Additionally, resonance dampingis highly desirable if it can be achieved while still allowing thenecessary flexibility of movement for roll and pitch while realizingrigidity against radial, circumferential and yaw motions.

Prior attempts to solve these problems are exemplified in U.S. Pat. Nos.3,931,641 and 4,167,765. to Watrous. Suspension assemblies have oftenbeen termed as winchester flexures and whitney suspension mechanisms.

In every suspension assembly, it is necessary to provide electricalconnections between the reading and writing head and an actuatorassembly. In making the electrical connection, the conductors andnecessary insulation should not adversely effect the performance of thesuspension assembly. Also, the point of connection between thesuspension assembly and the head itself should be made to eliminate orminimize any bias effects due to stiffness of the electrical connectionmeans. Patents such as Gordon et al U.S. Pat. No. 4,645,280 and PoormanU.S. Pat. No. 4,616,279 are representative of prior solutions toelectrical connection problems. Poorman, as an example, completelyremoves insulation from conductors in the area between the head and thesuspension assembly.

BRIEF SUMMARY OF THE INVENTION

The present invention solves the above mentioned problems by forming anovel suspension arm assembly which combines stainless steel with novel"composite" plastics including fiber reinforced polyetherimides andfilled or unfilled liquid crystal polymers or other plastics which havesufficient stiffness and damping properties. The plastics are selectedto provide excellent stiffness while providing damping which virtuallyeliminates resonance problems.

Previous suspension arm assemblies have been formed from stainless steelthroughout the structure. The flexures, load beams, spring and baseplates have all been formed of stainless steel. While the stainlesssteel provides excellent rigidity, it also gives rise to problems withresonance. The present invention provides a hybrid suspension assemblyutilizing the desirable properties of steel with speciality plasticsthat have inherent internal damping characteristics to create a superiorsuspension arm assembly.

In one form of the invention, the suspension arm assembly is comprisedof a plastic base plate, stainless steel spring, plastic load beam andstainless steel flexure. The plastic chosen for the load beam providesexcellent rigidity along the longitudinal axis of the load beam. Unlikestainless steel, the plastic load beam has excellent damping properties.

In an alternative form of the invention, the suspension arm assemblycomprises a single piece of stainless steel including a flexure whichextends through the length of the entire assembly. A plastic base plateis secured to the stainless steel on the end remote from the flexure anda plastic load beam element is secured to the stainless steel adjacentthe flexure and extending up toward the base plate. Like the otherembodiment of the invention, this suspension arm assembly has excellentrigidity and excellent dampening properties. Both allow the use of astainless ball bearing as a load protuberance which greatly decreasescosts in manufacturing and provides better tolerance control, and gimbalaction.

In both forms of the suspension arm assembly described above, electricalconnections extend between the base plate end and the flexure to connecta head which will be secured to the flexure. Preferably, the electricalconnections employ a flexible circuit consisting of conductive traceswhich are laminated in an insulating film. In order to minimize theheight of the suspension arm assemblies, it is possible to secure theflexible circuit to the suspension arm assembly by placing it betweenthe stainless steel components and the plastic components. This alsoeliminates the need for wire captures and center tangs, thus providing avery low profile suspension arm assembly. Alternately, wire capturegrooves could be molded into the load beam.

Another feature of the invention deals with the flexible circuit as itpasses from the suspension arm assembly to the head. In that region theflexible circuit is typically unsupported. That region is referred to asa pigtail due to its bent shape. In the pigtail region of the invention,a flexible circuit is utilized which minimizes the effect of theelectrical connection on the "flying" performance of the head. This isaccomplished by utilizing a very thin polyimide film base to which theconductive traces are adhered. It is also possible to copper clad thepolyimide base without adhesive. Fortin Industries, Inc., of Sylmar,Calif., produces a copper-polyimide composite under its brand nameFortin Microclad™ which is suitable herein. Other suppliers of suitablenon-adhesive composites include Andus of Canoga Park, Calif. Optionally,the conductors may be covered by a similar very thin polyimide film. Inthe most preferred form, cuts are made between each of the conductorsalong a portion of the pigtail such that each conductor may flexindependently of the other. Thus, each very small conductor remainsspaced from the others and does not act as a single, more rigid cablewhich would effect the flying performance of the head.

Another alternative for handling the circuitry is to adapt moldedcircuit board (MCB) technology to the hybrid suspension assemblycomponents of the invention. Photoselective plating processes may beutilized to add conductive traces to the composite plastics. Thecomposite plastic parts may be molded and prepared for ultravioletexposure of a photoimage followed by plating with copper. This dispenseswith plating resists. Other procedures form circuit traces in theplastic mold as raised lands. Fillers, added to the resin in the firstshot renders it plating catalytic. The first shot is then placed in asecond cavity and a second shot of noncatalytic resin is molded aroundit. Next, an adhesion promotion step is performed and, finally, a fullyadditive copper plating operation is conducted. There are a number ofother processes which will produce molded circuit boards. The methodsused therein may be utilized in making the novel hybrid suspensionassemblies of this invention.

Methods described in U.S. Pat. No. 4,698,907, the disclosure of which isincorporated herein by reference, may also be utilized to provide theelectrical pathway on the composite plastic parts of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description of the invention including its preferredembodiments are hereinafter described with specific reference being madeto the drawings in which:

FIG. 1 is a side elevation view of a hybrid suspension arm assembly ofthe invention;

FIG. 2 is a top view of the suspension arm assembly of FIG. 1;

FIG. 2A is a cross-sectional view through the base plate, spring andbarrel of FIG. 2 taken along lines 2A--2A;

FIG. 3 is a side elevation view of another embodiment of the hybridsuspension arm assembly invention;

FIG. 4 is a top view of the suspension arm assembly of FIG. 3;

FIG. 5 is a cross-sectional view through the base plate and spring ofFIG. 4 taken along line 5--5 to show the attachment of the base to thespring;

FIG. 6 is an exploded perspective showing an alternative method ofstaking the plastic to the metal components of the invention;

FIG. 6A is a cross-sectional view of the staked suspension of FIG. 6through line 6A--6A;

FIG. 7 is an exploded view of two suspension assemblies and means formounting to a single actuator arm;

FIG. 8 is a partial cross-sectional view of the invention of FIG. 7through line 8--8;

FIG. 9 is a perspective view of a pigtail electrical connection betweena head and the suspension assembly.

FIG. 10 is a cross-sectional view through the pigtail electricalconnection along lines 10--10.

FIG. 11 is a perspective view similar to FIG. 9 in which each conductoris isolated from the others; and

FIG. 12 is a perspective view similar to FIG. 11 in which the conductorform opposing loops;

FIG. 13 is a cross-sectional view of FIG. 12 taken through line 13--13through an alternative pigtail electrical connection.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 and 2, a novel hybrid suspension assembly 10is shown. Assembly 10 is comprised of a composite plastic base plate 12,spring 14, composite plastic load beam 16 and a flexure 18. Base plate12 is securable to an actuator arm (not shown) which may carry amultiplicity of head/suspension assemblies.

Base plate 12 and load beam 16 are each constructed of a compositeplastic which provides high unidirectional mechanical properties toprovide the rigidity required in suspension assemblies. Polyetherimides,which are amorphous high performance thermoplastics provide excellentrigidity, strength, dimensional stability and electrical properties.When suspension assemblies are made with suitable plastics reinforcedwith glass fiber or carbon fibers, polyetherimides should have betterperformance than the prior stainless steel suspension assemblies. Theplastics have a great advantage over stainless steel in that theirdamping properties are excellent. At resonance, the input amplitude ofthe base plate end would have to be increased 30 to 40 times to obtainan equivalent output amplitude of the flexure end for an all-steelsuspension assembly. Suitable polyetherimides are available from GeneralElectric Co. of Pittsfield, Mass. under the trademark ULTEM. Chemicallypolyetherimide is a 2.2-Bis (4-(3,4-dicarboxyphenol) phenyl) propanedianhydride-m-phenylene diamine copolymer. ULTEM 2000 series are glassreinforced with 10-40% glass. Dimensional stability and rigidity areexcellent.

The use of any of the composite plastics referred to herein provides asubstantial weight savings. A standard Whitney suspension currentlyweighs about 0.3 grams while the hybrid Whitney suspension can weigh aslittle as 0.195 grams. The lighter mass may reduce access time by eightpercent.

Other suitable composite plastics include liquid crystal polymers (LCP)which exhibit highly ordered structures. The morphology of LCP's isparticularly susceptible to orientation during processing. In solids,uniformly dispersed fiber-like aggregates are observed, formingwood-like structure described as self-reinforcing polymers. The veryhigh unidirectional mechanical properties of LCP are utilized in theload beam and base plate to replace previous stainless steelconstructions. The mechanical damping is excellent.

LCP's are available from Celanese Speciality Operations, CelaneseCorporation, Summit N.J. under the trademark Vectra™. Vectra brandresins are primarily aromatic co-polyesters based on p-hydroxybenzoicacid and hydroxy naphthoic acid monomers. Over 70 variants ofnaphthalene based resins are available including grades with fillerssuch as glass fibers, graphite flake, carbon fibers, mineral fibers andparticular fillers. LCPs under the trademark Xydar™ are available fromDartco Manufacturing Co. of Augusta, Ga. Xydar brand resins arepolyesters based on terephthalic acid, p,p'-dihydroxybiphenol andp-hydroxybenzoic acid. Filled and unfilled grades are available.Chemically, Xydar resins may be expressed as4,4'-Dihydroxydiphenyl-p-hydroxybenzoic acid terephthalic acid polymers.

Both base plate 12 and load beam 16 are preferably formed of compositeplastic in which the orientation or grain, if present, runs along thelongitudinal axis of the suspension assembly. Base plate 12 is connectedto load beam 16 via a stainless steel spring 14. It is also possible toform the base plate and load beam in one molding step, leaving a pair ofcomposite plastic stabilizer bars 20, 22 connecting the load beam 16 andbase plate 12. One piece units of base plate, load beam and stabilizersprovide for easier assembly. The stabilizer bars, if present, would neckdown as shown in FIG. 1 such that they function as a hinge and have aminimal pre-load effect.

The load beam 16 is connected to a stainless steel flexure 18. Flexure18 may present a substantially rectangular flexure having two parallel,flexible narrow fingers and a relatively stiff cross leg as shown anddesired in U.S. Pat. No. 3,931,641 or it may be a single piece having astiff cross leg offset to support a slider as shown in U.S. Pat. No.4,167,765. U.S. Pat. Nos. 3,931,641 and 4,167,765 are incorporatedherein by reference. Except for certain improvements referred to hereinregarding the flexure 18, any flexure designed to carry a slider or headmay be utilized in this invention.

As shown in FIG. 1, the base plate and load beam are secured to thestainless steel spring and flexure by ultrasonically or heat stakingplastic which extends through spaced openings through the steel members.The weld joints are generally designated as reference 26.

As shown in FIGS. 1, 2 and 2A, the inventive suspension assembly alsoincludes a novel connecting means for securing the assembly to anactuator assembly. The base plate includes a swagable barrel 30 capturedbetween openings through base plate 12 and spring 14. Barrel 30 may besimilar to a standard tubular rivet. Portion 32 of barrel 30 extendsbelow the suspension assembly such that it may be received in a matingaperture in an actuator arm. Connection may be then made by using ariveting device to expand portion 32. This greatly simplifies theprocess of connecting suspension assemblies to their mounts. Prior screwmounts are labor intensive and requires more expensive components.

A mechanism similar to the swagable barrel discussed above may beutilized to attach two suspension assemblies to one actuator arm. Asshown in FIGS. 7 and 8, a pair of suspension assemblies 10 are connectedto a single actuator arm 170. Actuator arm 170 has a hole 172 cuttherethrough. Each suspension assembly 10 has a composite plastic baseplate 174 which include molded fingers 176 which may extend through hole172 of the actuator arm 170. Fingers 176 are designed to distort uponbeing pushed through hole 172 and to snap back into position afterpassing through hole 172 as shown in FIG. 8. Each suspension assembly 10is snapped into position with the fingers 176 extending through bothsides of the actuator arm 170 as shown in FIG. 8. A ball 178 is thenpressed into hole 172 which forces the fingers 176 on each base plateagainst the inside of hole 172 in actuator arm 170. Ball 178 will fit agroove 184 in fingers 176. For even better gripping, the edges of theactuator arm 170 which define hole 172 may be serrated or splined 180.Thus, some of the plastic of the fingers 176 will tend to flow into thespaces formed by serrations or splines 180 by ball 178. This providesgood holding power, ease of installation and a low profile assembly andcan be removed by pressing the ball out of the pocket. Although shownwith two suspension assemblies 10, the method is usable to secure asingle assembly to an actuator arm.

Flexures require a load protuberance, typically formed as a dimple onthe center tongue of the flexure. The load protuberance contact the loadbeam and serves as a pivot point about which the head or slider maypitch and roll to follow the changing topography of the disk.

Rather than forming a dimple or load protuberance in the metal of theflexure, the present invention utilizes commercial ball bearings 40which are secured to the flexure. Ball bearings are inexpensive andeliminates the precision forming needed to make satisfactory formeddimples. Ball bearings have far better finishes and controlledgeometries than previous formed load protuberances. Dimple forming alsocauses a flatness problem in the tongue of the assembly. As shown, theball bearing 40 is embedded into the load beam such that the protrudinglower hemisphere may contact the flexure. The use of ball bearings for agimbal allows a lower gimbal point which provides greater stability andbetter flying characteristics. The ball bearing provides better tongueflatness control and the smoother dimple improves flying performance.

In another form of the invention, the spring and flexure are formed as asingle piece from stainless steel. With reference to FIGS. 3 and 4, itwill be seen that the suspension assembly 100 includes a compositeplastic base plate 102 and a composite plastic load beam 106 which maybe joined with a pair of plastic stabilizer bars 120, 122. However, asshown, the preload spring and flexure are formed in one piece,designated as element 128. Element 128 has a region 114 which functionsas a spring and a flexure 118. Flexure 118 preferably includes the novelball bearing load protuberance 140 as described above using ballbearings 40 of the invention. Element 128 is secured to the base plate102 and load beam 106 by ultrasonic weld or heat stake joints 126 in amanner as described previously. Alternatively, the composite plastic maybe staked over the steel which is coined to match the plasticconfiguration. See FIG. 6. The base plate may include the novel swagablebarrel as described previously.

With reference to FIG. 6, an alternative method of attaching thecomposite plastic elements to the steel elements of the suspensionassembly is shown. As shown, the composite plastic may be staked overthe steel which is coined to match the plastic configuration. Anultrasonic horn melts the composite plastic edges 108 down over thesteel to make a low profile mount. Heat or cold staking techniques mayalso be utilized depending on the plastic. Other means specific to theplastic may be employed.

The one piece spring and flexure shown as element 128 allows greaterprecision on critical dimensions of the assembly. The composite plasticload beam and base plate provide excellent rigidity and virtuallyeliminates resonance problems.

In both forms of the invention, circuitry between an actuator assemblyand the head is readily handled through the use of a flexible circuitconsisting of conductive traces and a flexible, insulating material suchas the polyimide sold under the trademark Kapton from E. I. du Pont deNemours of Wilmington, Del. The flexible circuitry is generally shown inthe figures as 150. As shown in FIGS. 9-13, circuitry 150 includesconductive traces 152 bonded to a thin layer of polyimide insulation154. Insulation layer 154 must be flexible and should not adverselyaffect the head performance or head load. Layer 154 is preferably formedfrom polyimide having a thickness of less than about 0.001 inches, andmost preferably, about 0.0005 inches. The conductors 152 are adhered tothe insulating layer by a modified acrylic adhesive 156. Of course, asstated previously, other methods of forming conductors on the insulatinglayer are included within the scope of this invention.

As referred to previously, the invention also involves the electricalconnection between the suspension arm and head 160. In the region inwhich the flexible circuit 150 is unsupported between the head 160 andload beam the circuit is referred to as a pigtail 190 due to its bentshape. As shown in FIG. 9, the pigtail 190 includes a twist 192 adjacentthe load beam end as shown. The twist 192 preferably should be adjacentto the load beam to minimize the effect on the flying performance of thehead 160.

FIG. 10 shows a cross-section through pigtail 190 of FIG. 9. It showsthe lower insulating layer 154 to which conductors 152 are attached. Asshown, conductors 152 are attached via acrylic adhesive 156. Othertechniques are suitable so long as conductive paths are on an insulatinglayer.

An alternative pigtail construction is shown in FIGS. 11 and 12. In FIG.11, each conductor 152 is physically separated from the other by havingthe lower polyimide layer 154 cut to form separate insulated conductors.If desired, a top layer of polyimide 158 may be applied above conductor152 with adhesive 156 as shown in FIG. 13. The loops 194 of the pigtailof FIG. 11 both lead to what is commonly referred to as a rotated or"sidewinder" head 186.

Typically, the conductors will be formed from a flat sheet of copperclad polyimide. Using photoresist methods, the copper is etched toremove undesired copper. Any adhesive exposed by the etching process maybe removed by plasma etching if desired. If desired, an upper layer ofpolyimide 158 may be adhered to the top, exposed copper as shown in FIG.10.

The pigtail construction of FIG. 12 differs from FIG. 11 in that thetwists 192 are in opposite direction such that the loops 190 areconfigured as shown. This construction tends to counter any effect thepigtail and twist may have in the flying performance of the head. In allcases, twist 192 involves a set in the polyimide and conductors close tothe load beam end remote from the head to minimize moment effects on thehead.

The flexible circuit 150 may be sandwiched between the stainless steeland plastic parts. This decreases the height of the suspension armassembly and simplifies the capture of the flexible circuit.

In considering this invention it must be remembered that the disclosureis illustrative only and that the scope of the invention is to bedetermined by the appended claims.

What is claimed is:
 1. A suspension arm assembly comprising:(a) a baseplate member constructed of a non-metallic composite plastic material;(b) a spring element joined to said base plate, said spring elementbeing substantially resilient adjacent to said base plate; (c) a loadbeam element constructed of a non-metallic composite plastic material,said load beam element being joined at one end to said spring elementand having a free end spaced from said one end, said load beam elementbeing substantially rigid along its length to present a loading force atsaid free end; and (d) a flexure member fastened to said free end ofsaid load beam element, said fixture including a load protuberance whichcontacts said load beam.
 2. The suspension arm of claim 1 wherein saidload protuberance is a ball bearing.
 3. The suspension arm of claim 1wherein said base plate member and said load beam element are connectedby a pair of spaced stabilizer bars, said stabilizer bars beingconstructed and arranged of the same composite plastic and functioningas hinge points across said spring element.
 4. The suspension armassembly of claim 1 further including electrical connection means forproviding electrical connections along the length of said assemblybetween said base plate and said flexure, said electrical connectionmeans including a plurality of electrical conductors encapsulated in anelectrically insulating film.
 5. The suspension assembly of claim 4further including head means secured to said flexure, said electricalconnection means being in electrical connection to said head means, saidelectrical means forming a pigtail bend having a twist near the end ofthe load beam between said flexure to said head.
 6. The suspensionassembly of claim 5 wherein said pigtail bend region of said electricalconnection means comprises a plurality of electrically separateconductive traces secured to a polyimide film base having a thickness ofless than about 0.001 inches.
 7. The suspension assembly of claim 5wherein said conductors in said pigtail bend are covered by a top layerof polyimide film having a thickness of less than about 0.001 inches. 8.The suspension assembly of claim 6 wherein the pigtail bend regionincludes cuts between each conductor running the length of the pigtailbend through the polyimide film and adhesive to provide greaterflexibility.
 9. The suspension arm assembly of claim 4 wherein saidelectrical conductors are sandwiched between said base plate and spring,said load beam and spring and said load beam and flexure.
 10. Thesuspension arm assembly of claim 6 wherein each conductor and itsinsulating base is separated from the other conductors and bases.
 11. Asuspension arm assembly comprising:(a) a base plate member constructedof a non-metallic composite plastic material; (b) a spring element beingjoined at one end to said base plate, said spring element beingsubstantially resilient adjacent to said base plate and including a freeend spaced from said one end, said spring element including a flexure atits free end, said flexure including a load protuberance; and (c) a loadbeam element constructed of a non-metallic composite plastic material,said load element being joined to said spring element between saidflexure and said base plate member, said load beam element being spacedfrom said base plate member such that said spring element therebetweenmay function as a spring element, said load beam element cooperatingwith said spring element where so attached such that the load beampresents a loading force at the free end of said spring element topresent a loading force against which said load protuberance may rest.12. The suspension arm of claim 11 wherein said load protuberance is aball bearing.
 13. The suspension arm of claim 11 wherein said base platemember and said load beam element are connected by a pair of spacedstabilizer bars, said stabilizer bars being constructed and arranged ofthe same composite plastic and functioning as hinge points across saidspring element.
 14. The suspension arm assembly of claim 11 furtherincluding electrical connection means for providing electricalconnections along the length of said assembly between said base plateand said flexure, said electrical connection means including a pluralityof electrical conductors encapsulated in an electrically insulatingfilm.
 15. The suspension assembly of claim 14 further including headmeans secured to said flexure, said electrical connection means being inelectrical connection to said head means, said electrical means forminga pigtail bend between said flexure to said head.
 16. The suspensionassembly of claim 15 wherein said pigtail bend region of said electricalconnection means comprises a plurality of electrically separateconductive traces secured to a polyimide film base having a thickness ofless than about 0.001 inches.
 17. The suspension assembly of claim 15wherein said conductors in said pigtail bend are covered by a top layerof polyimide film having a thickness of less than about 0.001 inches.18. The suspension of claim 17 wherein the pigtail bend region includescuts between each conductor running the length of the pigtail bendthrough the polyimide film and adhesive to provide greater flexibility.19. The suspension arm assembly of claim 14 wherein said electricalconductors are sandwiched between said spring and said base plate andload beam element.